http://i1153.photobucket.com/albums/p515/RPGTabbycat/ScreenShot12_zps1bc6ca5f.png
This happened completely by accident. I was using my bow from a distance to shoot Arvel down, and then I shot him. Once shot in the knee (or slightly below) killed him. Apparently it's a critical part of the body.
Anyone else have any "arrow to the knee" kills?